EVFs are inferior in the same way a big screen TV is inferior to a window - you can't improve on reality.

There are no cost savings benefitting the consumer - just check prices of mirror less.

There is no reliability issue with mirror boxes worth mentioning - I have cameras that are 30+ years that works fine. Most problem with old cameras are failure of electronics.

The space savings are small if you compare the sensor size. A 200 mm lens is the same size on a DSLR and mirror less.

Actually, I think the weight savings is there. A Sony A7 with 24-70 Zeiss is about 2lbs while the EOS5DMIII with similar lens is coming in at about 3.5 lbs. For me, losing that much weight and more for backpacking trips would be a godsend.

I think Nikon and Canon could easily counter with smaller and lighter SLRs and I'm sure they can lighten the lenses a bit. This may be their solution for the near term There already is an EOS APS DSLR (SL1) that's a mere 14 oz. and quite compact. There is no reason this trend couldn't continue.